1. Field of the Invention
This invention is related to an angular velocity sensor utilizing coriolis force.
2. Description of the Related Art
A typical angular velocity sensor that uses coriolis force comprises a substrate, a mass portion, an excitation member, a beam and a detecting member. The excitation member forcefully exits the mass portion in an excitation direction. One end of the beam is connected to the mass portion while the other end thereof is fixed to the substrate. The detecting member detects the vibration of the mass portion. The beam is capable of flexibly fluctuating in the excitation direction as well as in a detecting direction, and supports the mass portion so as to enable the mass portion to move in the excitation direction as well as in the detection direction.
The excitation member typically is composed of segmented electrode. The segmented electrode comprises movable electrode that is arranged on the mass portion side, and fixed electrode that is arranged on the substrate side. When an alternating current voltage is applied to the segmented electrode, electrostatic attraction is generated between the movable electrode and the fixed electrode, thereby enables the mass portion to vibrate in the excitation direction.
The detecting member is typically a capacitor that is configured of a plane electrode arranged on the mass portion side and another plane electrode arranged on the substrate side. The plane electrodes on the mass portion side and the substrate side face each other along the detecting direction.
In this type of angular velocity sensor, in a case where angular velocity is applied to the mass portion while it is being excited in the excitation direction, a coriolis force occurs in a direction (i.e. the detecting direction) that is orthogonal to both the excitation direction of the mass portion and an axial direction of rotation of the angular velocity, which forces the mass portion to waver in the detecting direction. In such a case, due to the vibration of the mass portion in the detecting direction, the distance between the plane electrodes on the mass portion side and the substrate side which constructs the capacitor, i.e. the detecting member, is thereby changed; consequently, this change in the distance causes the electrostatic capacitance of the capacitor to modulate. The angular velocity sensor detects the vibration of the mass portion in the detecting direction from the aforesaid modulation of electrostatic capacitance, and utilizes the detection results in the calculation of the angular velocity that had been applied on the angular velocity sensor. Such type of angular velocity sensor is disclosed in Japanese Patent Application Publication Nos. 1-170276 and 2005-292125.